Advances in fabrication technologies for semiconductors and display apparatus have led to the rapid development of multi-media. In fact, thin-film transistor liquid crystal displays (TFT-LCDs) have gradually dominated the display market due to their high picture quality, better spatial utilization rate, low power consumption, and radiation-free operation.
At present, a liquid crystal display in the marketplace may have a high contrast ratio, no gray scale inversion, low color shift, high luminance, wide color gamut, high color saturation, rapid response time, and a wide viewing angle. The techniques currently capable of providing a wide viewing angle include twisted nematic (TN) liquid crystals together with a wide viewing film, in-plane switching (IPS) liquid crystal display, fringe field switching liquid crystal display, and multi-domain vertical alignment (MVA) liquid crystal display (LCD).
Conventional MVA-LCD panels include an active element array substrate, an opposite substrate, and a liquid crystal layer disposed between the two substrates. A pixel electrode may be formed on one side of the active element array substrate and a common electrode layer may be formed on one side of the opposite substrate. Furthermore, a first polarizing film is disposed on the side of the active element array substrate opposite the pixel electrode and a second polarizing film is disposed on the side of the opposite substrate opposite the common electrode layer. Generally, in the absence of an electric field, the liquid crystal molecules in the liquid crystal layer align perpendicular to the two substrates. But when an electric field is applied between the two electrodes, the liquid crystal molecules tilt.
FIGS. 1A and 1B depict top views of a pixel electrode 110 and a common electrode layer 120 respectively of a single pixel unit in a conventional MVA-LCD panel. Referring to FIG. 1A, in addition to illustrating the pixel electrode 110, a scan line, a data line, and an active element (all unnumbered) are also illustrated. In practice, the pixel electrode, scan line, data line, and active element may be formed on the active element array substrate. But to show the relative positions of these components with respect to the common electrode layer 120, the scan line, data line, and active element are also illustrated in FIG. 1B. Although polarizing films are not shown in FIGS. 1A and 1B, FIG. 1A (and FIGS. 1C and 2) does show the transmission axis for the first and second polarizing films, which are in the X and Y directions, respectively.
In the conventional MVA-LCD panel, the pixel electrode 110 (FIG. 1A) has a plurality of main slits 112 and a plurality of fine slits 114, and the common electrode layer 120 (FIG. 1B) also has a plurality of main slits 122 and a plurality of fine slits 124. Because the directions of the electric fields near the main slits 112, 122 and the fine slits 114, 124 are different from other portions of the pixel, the direction of inclination of the liquid crystal molecules will have more variations. Thus, the viewing angle of the liquid crystal panel is improved. Dark streaks, however, may form in the areas R10 and R12.
For example, referring to the FIG. 1A, the edge of the pixel electrode 110 in the areas R10 and R12 are straight lines that extend in a direction that is different from the direction that the main slits 112 and the fine slits 114 extend. Thus, the forces acting on the liquid crystal molecules 130 in these areas are in different directions, which prevent them from being driven in a suitable direction. The forces exerted on the liquid crystal molecules 130 within the area R12 are illustrated in FIG. 2. For example, the edge of the pixel electrode 110 exerts the force at F12 on the liquid crystal molecules 130 and the fine slits 114 exert the force at F14 on the liquid crystal molecules 130. Because the forces at F12 and F14 are in different directions, the liquid crystal molecules 130 in the area R12 are not driven in the desired direction F14. Thus, dark streaks are likely to occur in this area. Although FIG. 2 shows the forces exerted on the liquid crystal molecules 130 in the area R12, a similar problem with forces that are exerted in different directions occurs in the areas R10, which may also result in dark streaks.
To address the problem of dark streaks, auxiliary-slits 126 are formed in the common electrode layer 120. As is shown in FIG. 1B, the auxiliary-slits 126 are formed in the areas R10 and R12 and they are parallel to the edge of the pixel electrode 110. Because the force exerted on the liquid crystal molecules in the area R12 by the auxiliary-slit 126 (FIG. 2 at F16) points to the positive X direction and the force F12 points to the negative X direction, the resulting force acting on the liquid crystal molecules 130 is closer to the direction of the force F14. Thus, the probability of generating dark streaks in area R12 (and areas R10) is lowered.
In the process of manufacturing an MVA-LCD panel, the pixel electrode 110 and common electrode layer 120 are formed separately on the two substrates. Thereafter, the two substrates are aligned and assembled so the pixel electrode 110 and the common electrode layer 120 are disposed to face each other as is shown in FIG. 1C. If, however, the pixel electrode 110 and the common electrode layer 120 are not properly aligned during MVA-LCD panel assembly, dark streaks may still appear because the auxiliary-slits 126 do not produce the desired effect on the liquid crystal molecules within the areas R10 and R12. As a result, the display quality (such as the transmittance and response time) of the multi-domain vertical alignment liquid crystal display panel will be substantially compromised.
Accordingly, there is a need for a multi-domain vertical alignment liquid crystal display panel that resolves display quality deterioration problems.